The ultimate goal of the project is to determine measurable, sensitive, and specific biomarkers for oxidative damage in rodents, nonhuman primates and humans. An initial study of carbon tetrachloride-dosed rats was conducted to compare and evaluate different assays in the assessment of oxidant stress status in vivo. Ozone exposure to rats was used as a second model of oxidative stress. Sufficient samples of biological specimens (blood and urine) taken from rats over three time points and three doses of exposure were provided to 20 investigators worldwide. A battery of oxidative stress measurements- isoprostanes, protein oxidation, protein carbonyls, o-tyrosine, m-tyrosine, nitrotyrosine, dityrosine, chlorotyrosine, 8-hydroxydeoxyguanosine (8-OHdG), Single Cell Gel (SCG)/comet assay, GSH/GSSG, thiobarbituric acid reactive substances (TBARS), aldehydes from lipid peroxidation, lipid hydroperoxides, free radical generation and antioxidants were run on each sample by investigators from 20 labs outside NIEHS and 5 labs from NIEHS. At present, results from the model of carbon tetrachloride poisoning have been completed. As shown by the statistical analyses, carbon tetrachloride poisoning increased the generation of isoprostanes and MDA in plasma and urine in time- and dose-dependent manners. Therefore, changes in these markers are indicative of oxidative stress. It was also found that plasma antioxidants can not be used as markers of oxidative stress in a model of acute carbon tetrachloride poisoning. Collecting data from the ozone exposed animals is still in progress.